Hi Elizabeth,
Thank you for your response.
I have searched all indexes via Ancestry.com. AlsoShipping lists State records NSW and numerous Irish immigration records.
Today I have just received the death certificate of Robert Currans father of Rachel Kidd Currans.When he died in 1862, he had been in Australia "ten years". This means that he must have arrived just before Rachel and George Frederick Francis got married in 1852!!

In the Argus Newspaper of 26 May 1852 a Testimonial was published to Captain Reid, captain of the 'Lady Harvey', who took ill on a voyage from Adelaide to Melbourne. The testimonial was signed by some of his passengers on the 21 May 1852. Robert Currans Sen. and Robert Currans Jun. were two of the signatories.
If you would like to view the article, in Trove; to make your search easier, I have tagged it - Robert Currans voyage

The 145 ton fast sailing brig Lady Harvey was expressly fitted out to carry steerage passengers and of course the mail from Adelaide to Melbourne.
In 1852, Many, many more ships were leaving Adelaide on a daily basis for the diggings in Victoria. With the gold rush in 1852, up to 150 vessels a day, of every description were anchored in Hobsons Bay. (Vic) So if these are your CURRANS you're lucky to have found their arrival in Victoria.
Now to find an arrival in South Australia, probably not long before.